Twenty-one patients with advanced metastatic adenocarcinoma of the colon or rectum were treated with a combination of intravenous Methyl CCNU and Ftorafur, an analogue of 5-fluorouracil. In addition, 13 patients were randomized to receive MER. Two previously untreated patients, neither of whom had received MER, achieved partial remissions lasting 9 to 31 weeks. Neither patient had hepatic involvement with disease. Four patients had stabilization of disease lasting up to 14 weeks. Three of these patients had received MER. Hematologic toxicity of this regimen was severe with 65% of all patients treated having platelet counts below 100,000/mm3 at some time during the course of therapy. 33% of patients had white blood cell counts of 2,000/mm3 at some time during therapy. Although others have reported optimistic results from similar drug combinations, the results of this study are not encouraging. It is postulated that hepatic conversion of ftorafur to 5-FU may occur less well in patients with hepatic dysfunction. Further studies of ftorafur metabolism in humans are needed.